Oral care compositions, such as oral care compositions comprising water, may be susceptible to bacterial growth. A high water content fosters the growth of bacteria in an oral care composition, and consequently shortens the shelf-life of the composition, resulting in consumer dissatisfaction. Therefore, oral care compositions comprising a high water content may incorporate additional preservative ingredients into their formulations, such as benzyl alcohol, aldehydes, methylparaben, and propylparaben.
Additionally, many oral care compositions may comprise expensive ingredients, such as ingredients that are naturally occurring and may be limited in the environment. One such ingredient is carrageenan, which is a thickening agent that may be extracted from red seaweeds. Therefore, an oral care composition comprising a high content of carrageenan as a thickening agent may be expensive to manufacture, and it may be desirable from a cost standpoint to formulate compositions comprising suitable alternative ingredients.
Water, of course, is a cost-effective ingredient, and therefore maximizing its content in an oral care composition's formulation may decrease the cost associated with producing that formulation, as the content of other, more expensive, ingredients may consequently by replaced by the increased water content. Accordingly, it is desirable to increase the water content of a composition without adversely affecting the composition's micro robustness, or ability to inhibit bacterial growth. Furthermore, it is desirable to increase the water content of a composition without the need to incorporate additional preservative ingredients into the formulation.
Arriving at the ideal water content, however, can be complicated when formulating oral care compositions. Reducing the level of water, and optionally replacing some or all of the removed water with a humectant, for example, may create problems in obtaining acceptable theology and thickening properties in the composition. When water, which is a highly polar solvent, is removed, conventional thickening agents, such as carboxymethylcellulose, tend to gel up inadequately. Such formulations have been shown to exhibit progressive thickening over time, which prolongs the time period to reach a theological steady state, or even prevents the dentifrice from reaching a rheological steady state altogether. If a formulation routinely increases in viscosity over time, dispensing of the formulation will become difficult, which will likely result in consumer dissatisfaction.
One method known in the art for increasing the water content while improving micro robustness involves the addition of water soluble stannous ions to an oral care composition. The stannous ions may be chosen from the group consisting of stannous chloride, stannous pyrophosphate, stannous formate, stannous acetate, stannous gluconate, stannous lactate, stannous tartrate, stannous oxalate, stannous malonate, stannous citrate, stannous ethylene glyoxide, and mixtures thereof. Stannous ions, however, such as SnCl2, may be astringent compounds having a poor taste that would be unpleasant to a consumer.
Accordingly, it is desirable to formulate an oral care composition that is cost-efficient, has a high water content, desirable rheological properties, and maintains high micro robustness while being free of stannous ions.